Which of these numbers is prime? ${29,\ 33,\ 36,\ 51,\ 95}$
A prime number has exactly two factors: 1 and itself. The factors of 29 are 1 and 29. The factors of 33 are 1, 3, 11, and 33. The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, and 36. The factors of 51 are 1, 3, 17, and 51. The factors of 95 are 1, 5, 19, and 95. Thus, 29 is a prime number.